FM DXing using Spectrum-Lab as variable filter and demodulator

Will a good filter fix the splatter problem caused by strong adjacent signals?

Many DXers assume a good filter that is narrow and steep will solve all problems with strong signals on adjacent channels. Better look at the spectrum and discover the limitations.

This spectrum of my semi-local 94,4 NDR-Kultur shows during silent periods:
·Bessel function products of the pilot tone at 19, 38 and 57 kHz  
·57kHz RDS signal with surpressed carrier (Note: the 3x 19 kHz sits right in the gap of the surpressed carrier)  
·broadcaster internal used data digital signal above 60kHz, also using surpressed carrier  

These are only visible when the tx uses no audio compressor

At -100kHz the weak signal of 94,3 rs2 in Berlin (370km) is visible, this is my wanted signal.
Obviously the 94,4 spectrum reaches far into the 94,3 bandwidth.
Can we use a 80kHz filter for 94,3 ?

Watch the video at the page bottom.

Now I tuned with 80kHz bandwith to the wanted 94,3. It is very weak and the 94,4 spectrum reaches far into our bandwith. Audio sounds awful and entirely covers the wanted 94,3 audio.  
Now I reduced the bandwith to about 30kHz, the 94,3 tx becomes audible but with distortion, at least I am able to hear the wanted station. Fortunately German stations use a smaller deviation, stations with larger modulation become unintelligible with this narrow bandwidth  
In this situation the Sony XDR fails to recover the wanted audio, even worse, the XDR produces now the clear audio of 94,4 but with lower volume leaving the impresion that you hear NDR-Kultur on 94,3 which is not true.  
Once the 94,3 signal becomes stronger and exceeds a threshold, the XDR will lock on it and produce proper audio.  
This nicely demonstrates that a good filter alone cannot remedy the problem of adjacent splatter. A smarter way of demodulation is needed.  
These videos demonstrate some real-world reception and how to get the best out of it.  

Please click on full screen mode when it plays to watch it in max. resolution. (via right click)  

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